Sensing Devices and Manufacturing Methods Therefor

ABSTRACT

A sensing device is provided. The sensing device includes a sensing pixel array and a memory unit. The sensing pixel array is formed in a substrate and includes a plurality of pixels for sensing light. The substrate has a first side and a second side opposite to the first side and receives the light through the first side for sensing the light. The memory unit is formed on the second side of the substrate for memorization.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sensing device, and more particularly to asensing device with back-side illumination which comprises a memory unitdisposed on the front side of a sensing pixel array.

2. Description of the Related Art

Conventional image sensors comprises several elements that are key toenhance performance of the image sensors (e.g. CMOS image sensor, CIS),such as color filters, a sensing pixel array which converts light intoelectrical signals, circuits which receive electrical signals, convertelectrical signals to digital signals, and then process the digitalsignals, and etc. CIS technology is advantageous in that it may be usedto integrate all of the above mentioned elements on a single die orchip.

FIG. 1 shows a cross section of a conventional CMOS image sensor withfront-side illumination (FSI). Referring to FIG. 1, a CMOS image sensor1 comprises a pixel array 10 composed of pixels 100, a plurality ofmetal layers 11 forming CMOS circuits, a color filter 12, and amicrolens 13. The metal layers 11 are formed on the pixel array 10 forinterconnections. The color filter 12 is formed on the metal layers 11.The CMOS image sensor 1 receives light 14 through the microlens 13, andthe received light is transmitted to the pixel array 10 through thecolor filter 12 and the metal layers 11. Since the CMOS image sensor 1with front-side illumination requires several light sensing regionswhich are not blocked by metal lines in the metal layers 11 for agreater aperture ratio, severe restrictions are made at the metal linesconnecting the in-pixel circuitry to the peripheral circuitry. Theselimitations to the metal line interconnection between the pixels 100 andthe periphery circuitry limit the maximum bandwidth available forpixel-to-periphery communications. Accordingly, parameters, such asmaximum frame rate, dynamic range, etc. of the CMOS image sensor areworsened. Moreover, when the size of the pixels 100 becomes smaller, theperformance of the pixel array 10 including quantum efficiency (QE),cross-talk effect, and dark current is degraded.

Thus, back-side illumination (BSI) for CMOS image sensors has beendisclosed. FIG. 2 shows a cross section of a conventional CMOS imagesensor with back-side illumination. Referring to FIG. 2, a CMOS imagesensor 2 comprises a pixel array 20 composed of pixels 200, a pluralityof metal layers 21 forming CMOS circuits, a color filter 22, and amicrolens 23. The pixel array 20 receives light 24 through the microlens23 and the color filter 22 and not through metal layers 21. Theperformance of the pixel array 200 is not hindered by light passingthrough the metal layers 21, as light passes through the microlens 23and the color filter 22.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment of a sensing device is provided. The sensingdevice comprises a sensing pixel array and a memory unit. The sensingpixel array is formed in a substrate and comprises a plurality of pixelsfor sensing light. The substrate has a first side and a second sideopposite to the first side and receives the light through the first sidefor sensing the light. The memory unit is formed on the second side ofthe substrate for memorization.

In some embodiments, the memory unit comprises a first metal layer, asecond metal layer, a plurality of first metal lines, and a plurality ofsecond metal lines. The first and second metal layers are formed on thesecond side of the substrate. The memory unit is formed in the first andsecond metal layers. The first metal lines are formed in the first metallayer. The second metal lines are formed in the second metal layer andinterlaced with the first metal lines. Each set of the interlaced firstand second metal lines forms a cell for memorization. When data has beenwritten into one cell for memorization, the first metal linecorresponding to the cell is connected to a corresponding second metalline through a via, and, thus, the voltage levels of the first andsecond metal lines are equal.

An exemplary embodiment of a manufacturing method for a sensing deviceis provided. The manufacturing method comprises the steps of providing asubstrate, forming a sensing pixel array in the substrate, wherein thesubstrate has a first side and a second side opposite to the first side,and the sensing pixel array receives the light through the first sidefor sensing the light; and forming a memory unit on the second side ofthe substrate for memorization.

In some embodiments, the step of forming the memory unit comprises:forming a first metal layer and a second metal layer on the second sideof the substrate; forming a plurality of first metal lines in the firstmetal layer; and forming a plurality of second metal lines in the secondmetal layer. The second metal lines are interlaced with the first metallines, and each set of the interlaced first and second metal lines formsa cell for memorization. Moreover, data is written into one cell formemorization by connecting a corresponding first metal line to acorresponding second metal line through a via.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a cross section of a conventional CMOS image sensor withfront-side illumination;

FIG. 2 is a cross section of a conventional CMOS image sensor withback-side illumination;

FIG. 3 is a cross section of an exemplary embodiment of a sensingdevice;

FIG. 4 is an upward view of the sensing device 3; and

FIG. 5 is a flow chart of an exemplary embodiment of a manufacturingmethod for a sensing device.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIG. 3 is a cross section of an exemplary embodiment of a sensingdevice. Referring to FIG. 3, a sensing device 3 comprises a pixel array30, a plurality of metal layers 31, a color filter 32, and a microlens33. The pixel array 30 is formed in a substrate 310 and comprises aplurality of pixels 300, which are disposed in rows and columns, forsensing light. The substrate 310 has a first side 30 a and a second side30 b opposite to the first side 30 a. In the embodiment, the sensingdevice 3 uses back-side illumination (BSI) techniques. Thus, themicrolens 33 is formed on the first side 30 a of the substrate 310, andthe color filter 32 is formed between the microlens 33 and the sensingpixel array 30. In another example, the microlens 33 can be formedbetween the color filter 32 and the sensing pixel array 30. The metallayers 31 are formed on the second side 30 b of the substrate 310.Accordingly, the sensing pixel array 30 receives light 34 passingthrough the microlens 33 and the color filter 32 on the first side 30 afor sensing the light 34. Thus, the light 34 is not blocked by the metallayers 31 on the second side 30 b.

In the embodiment, four metal layers 31 ₁˜31 ₄ are given as an example.However, the number of metal layers may be determined according torequirements. Among the four metal layers 31 ₁˜31 ₄, two metal layersare used to form a memory unit. For example, as shown in FIG. 3, themetal layers 31 ₁ and 31 ₂ are used to form a memory unit 35 formemorization. In the embodiment, the memory unit 35 is implemented by aread-only memory (ROM). FIG. 4 is an upward view of the sensing device3. For clear description, FIG. 4 only shows the sensing pixel array 30and the memory unit 35 formed in the metal layers 31 ₁ and 31 ₂ in FIG.3. Referring to FIG. 4, the memory unit 35 comprises a plurality offirst metal lines ML1 ₁˜ML1 _(M) formed in the metal layer 31 ₁ and aplurality of second metal lines ML2 ₁˜ML2 _(N) formed in the metal layer31 ₂, wherein M and N are positive integers. The first metal lines ML1₁˜ML1 _(M) are interlaced with the second metal lines ML2 ₁˜ML2 _(N).Accordingly, each set of the interlaced first and second metal linesforms a cell for memorization. For example, the interlaced first andsecond metal lines ML1 ₁ and ML2 ₁ form a cell 350 ₁.

In some embodiments, the first metal lines ML1 ₁˜ML1 _(M) are formed inthe metal layer 31 ₂ and the second metal lines ML2 ₁˜ML2 _(N) areformed in the metal layer 31 ₁.

Referring to FIG. 4, the sensing device 3 further comprises a readoutcircuit 37 and a memory control circuit. The memory control circuitincludes a row decoding circuit 38, a column decoding circuit 39, and adecision circuit 40. As described above, the pixels 300 of the sensingpixel array 30 sense the light 34 passing through the microlens 33 andthe color filter 32. The pixels 300 thus generate detection signals DSrespectively according to the sensed light 34. The readout circuit 37 isused to read the detection signal DS which is generated from the atleast one selected pixel.

In the embodiment, the memory unit 35 is an ROM for memorizing data.When data has been written into one cell for memorization. acorresponding first metal line in the metal layer 31 ₁ is connected to acorresponding second metal line in the metal layer 31 ₂ through a via.For example, when data has been written into the cell 350 ₂ formemorization, the first metal line ML1 ₁ is connected to a second metalline ML2 ₄ through a via V1 ₄. The cell without a corresponding firstmetal line in the metal layer 31 ₁ connected to a corresponding secondmetal line in the metal layer 31 ₂ through a via does not memorize data.

The row decoding circuit 38 receives an address signal AS_(ROW) andselects one of the first metal lines ML1 ₁-ML1 _(M) once, according tothe address signal AS_(ROW), to detect a voltage level of the selectedfirst metal line. The column decoding circuit 39 receives an addresssignal AS_(COLUMN) and selects one of the second metal lines ML2 ₁˜ML2_(N), according to the address signal AS_(COLUMN), to detect a voltagelevel of the selected second metal line. The decision circuit 40 thendetermines whether the voltage level of the selected first metal line isequal to the voltage level of the selected second metal line. Assumethat the row decoding circuit 38 has selected the first metal line ML1 ₁according to the address signal AS_(ROW) to detect the voltage level ofthe first metal line ML1 ₁, and the decoding circuit 39 has selected thesecond metal line ML2 ₄ to detect the voltage level of the second metalline ML2 ₄ according to the address signal AS_(COLUMN). Since the firstmetal line ML1 ₁ is connected to the second metal line ML2 ₄ through thevia V1 ₄ for data writing, the decision circuit 40 determines that thevoltage level of the first metal line ML1 ₁ is equal to the voltagelevel of the second metal line ML2 ₄. Thus, the decision circuit 40decides that data has been written into the cell 350 ₂ for memorizationand generates a corresponding value, such as a logic high value “1”.

Assume that the row decoding circuit 38 has selected the first metalline ML1 ₁ according to the address signal AS_(ROW) to detect thevoltage level of the first metal line ML1 ₁, and the decoding circuit 39has selected the second metal line ML2 ₁ to detect the voltage level ofthe second metal line ML2 ₁ according to the address signal AS_(COLUMN).Since the first metal line ML1 ₁ is not connected to the second metalline ML2 ₁ through a via, the decision circuit 40 determines that thevoltage level of the first metal line ML1 ₁ is not equal to the voltagelevel of the second metal line ML2 ₁. Thus, the decision circuit 40decides that data is not written into the cell 350 ₁ and generates acorresponding value, such as a logic low value “0”.

According to the sensing device 3 of the embodiment, the sensing pixelarray 30 receives the light 24 through the first side 30 a of thesubstrate 310 for sensing the light 34, and the memory unit 35 formed inthe metal layers 31 ₁ and 31 ₂ is disposed on the second side 30 bopposite to the first side 30 a. Thus, the light 34 is not blocked bythe first metal lines ML1 ₁˜ML1 _(M) in the metal layer 31 ₁ and thesecond metal lines ML2 ₁˜L2 _(N) in the metal layer 31 ₂. Moreover, thefurther implemented memory unit 35 can memorize data, without degradingquantum efficiency (QE), cross-talk effect, and dark current of thesensing device 3.

FIG. 5 is a flow chart of an exemplary embodiment of a manufacturingmethod for a sensing device. In the following, the manufacturing methodis described by referring to FIGS. 3-5. In FIG. 5, a substrate 310 isprovided (step S50), and the sensing pixel array 30 is formed in thesubstrate 310 (step S51). The sensing pixel array 30 comprises pixels300 disposed in rows and columns. The metal layers 31 ₁ and 31 ₂ areformed on the second side 30 b of the substrate 310 (step S52). Then,the first metal lines ML1 ₁˜ML1 _(M) are formed in the metal layer 31 ₁(step S53), and the second metal lines ML2 ₁˜ML2 _(N) are formed in themetal layer 31 ₂ (step S54). The first metal lines ML1 ₁˜ML1 _(M) areinterlaced with the second metal lines ML2 ₁˜ML2 _(N), and each set ofthe interlaced first and second metal lines forms a cell of the memoryunit 35 for memorization. Data is written into one cell for memorizationby connecting a corresponding first metal line in the metal layer 31 ₁to a corresponding second metal line in the metal layer 31 ₂ through avia. The row decoding circuit 38 is disposed to select one of the firstmetal lines ML1 ₁˜ML1 _(M) according to the address signal AS_(ROW) todetect the voltage level of the selected first metal line. The columndecoding circuit 39 is disposed to select one of the second metal linesML2 ₁˜ML2 _(N) according to the address signal AS_(COLUMN) to detect thevoltage level of the selected second metal line. The decision circuit 40is disposed to determine whether the voltage level of the selected firstmetal line is equal to the voltage level of the selected second metalline. When the decision circuit 40 determines that the voltage level ofthe selected first metal line is equal to the voltage level of theselected second metal line, the decision circuit 40 decides that datahas been written into the corresponding cell and generates acorresponding value, such as a logic high value “1”. When the decisioncircuit 40 determines that the voltage level of the selected first metalline is not equal to the voltage level of the selected second metalline, the decision circuit 40 decides that data is not written into thecorresponding cell and generates a corresponding value, such as a logiclow value “0”. Then, the first side 30 a of the substrate 310 is groundto reduce the thickness of the substrate 310 (step S55). The microlens33 and the color filter 32 are formed on the first side 30 a of thesubstrate 310 (step S56). Accordingly, the sensing pixel array 30receives the light through the microlens 33 and the color filter 32.

In the step S56, the color filter 32 is formed between the microlens 33and the substrate 310. In some embodiments, the microlens 33 can beformed between the color filter 32 and the substrate 310.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. A sensing device comprising: a sensing pixel array, formed in asubstrate, comprising a plurality of pixels for sensing light, whereinthe substrate has a first side and a second side opposite to the firstside, and the sensing pixel array receives the light through the firstside for sensing the light; and a memory unit formed on the second sideof the substrate for memorization.
 2. The sensing device as claimed inclaim 1, wherein the memory unit comprises: a first metal layer formedon the second side of the substrate; a second metal layer formed on thesecond side of the substrate, wherein the memory unit is formed in thefirst and second metal layers; a plurality of first metal lines formedin the first metal layer; and a plurality of second metal lines formedin the second metal layer and interlaced with the first metal lines;wherein each set of the interlaced first and second metal lines forms acell for memorization.
 3. The sensing device as claimed in claim 2,wherein, when data has been written into one cell for memorization, thefirst metal line corresponding to the cell is connected to acorresponding second metal line through a via.
 4. The sensing device asclaimed in claim 2 further comprising: a first decoding circuit forreceiving a first address signal and selecting one of the first metallines once, according to the first address signal, to detect a voltagelevel of the selected first metal line; a second decoding circuit forreceiving a second address signal and selecting one of the second metallines, according to the second address signal, to detect a voltage levelof the selected second metal line; and a decision circuit fordetermining whether the voltage level of the selected first metal lineis equal to the voltage level of the selected second metal line; whereinwhen the decision circuit determines that the voltage level of theselected first metal line is equal to the voltage level of the selectedsecond metal line, the decision circuit decides that data has beenwritten into the corresponding cell.
 5. The sensing device as claimed inclaim 1, wherein the pixels are disposed in rows and columns, and thesensing device further comprises: a readout circuit for reading adetection signal which is generated from at least one of the pixelsaccording to the sensed light.
 6. The sensing device as claimed in claim1, wherein the sensing device uses back-side illumination techniques. 7.The sensing device as claimed in claim 1 further comprising: a microlensand a color filter formed on the first side of the substrate; andwherein the sensing pixel array receives the light through the microlensand the color filter.
 8. A manufacturing method for a sensing devicecomprising: providing a substrate; forming a sensing pixel array in thesubstrate, wherein the substrate has a first side and a second sideopposite to the first side, and the sensing pixel array receives thelight through the first side for sensing the light; and forming a memoryunit on the second side of the substrate for memorization.
 9. Themanufacturing method as claimed in claim 8, wherein the step of formingthe memory unit comprises: forming a first metal layer and a secondmetal layer on the second side of the substrate; forming a plurality offirst metal lines in the first metal layer; and forming a plurality ofsecond metal lines in the second metal layer; wherein the second metallines are interlaced with the first metal lines, and each set of theinterlaced first and second metal lines forms a cell for memorization.10. The manufacturing method as claimed in claim 9, wherein data iswritten into one cell for memorization by connecting a correspondingfirst metal line to a corresponding second metal line through a via. 11.The manufacturing method as claimed in claim 8, wherein the sensingdevice uses back-side illumination techniques.
 12. The manufacturingmethod as claimed in claim 8 further comprising: grinding the first sideof the substrate; and forming a microlens and a color filter on thefirst side of the substrate; wherein the sensing pixel array receivesthe light through the microlens and the color filter.
 13. Themanufacturing method as claimed in claim 12, wherein the color filter isformed between the microlens and the substrate.
 14. The manufacturingmethod as claimed in claim 12, wherein the microlens is formed betweenthe color filter and the substrate.